Energy & Fuels 1989, 3, 85-88
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Quantitative Mineral Distributions in Green River and Rundle Oil Shales G. Brons* and M. Siskin* Corporate Research Science Laboratory, Exxon Research and Engineering Company, Annandale, New Jersey 08801
R. I. Botto Exxon Research and Engineering Company, P.O. Box 4255, Baytown, Texas 77522
N. Guven Department of Geosciences, Texas Tech University, P.O. Box 4109, Lubbock, Texas 79409 Received March 7, 1988. Revised Manuscript Received October 19, 1988
A method for quantifying the mineral compositions of Green River and Rundle Ramsay Crossing oil shales based on X-ray diffraction (XRD) in combination with elemental analysis is described. After identification of the minerals in the starting oil shale by XRD, the mineral composition of products from reaction variable studies can be calculated from the elemental analysis. This procedure is only applicable to studies in which chemical/phyical treatment does not alter the mineralogy (e.g. sink-float separations). This approach also allows for quantification of organic matter content, which is otherwise problematic in clay-rich resources. Introduction A method using normative calculations has been developed to quantify the complex mineral composition of Green River (Colony Mine, Parachute Creek, CO) and Rundle (Lower Ramsay Crossing seam) oil shales. The method uses X-ray diffraction (XRD) in combination with elemental analysis (Elanal). In a previous report,l we described the beneficiation of Green River oil shale using aqueous ammonium sulfate at 85 "C in the presence of an insoluble organic solvent (toluene). The final reaction mixture consisted of three layers: a mineral or sink fraction; the aqueous phase containing unreacted ammonium sulfate plus carbonate mineral dissolution products; and an organic matter layer, or float fraction, containing dispersed swollen kerogen and some entrained minerals. Analysis of the aqueous layer for water-soluble salts and for calcium and magnesium contained in calcite and dolomite was routine. Quantification of the minerals found in the sink and float fractions was not as straightforward. The beneficiation treatment does not alter the mineralogy of the shale, other than carbonate mineral decomposition, and therefore provides excellent samples for the XRD/ Elanal approach. Minerals present in each fraction were quantified by first identifying the minerals present in the starting shale by XRD. The semiquantitative mineral distributions were computed by using peak area normalizations. Quantification of mineral phases in both the sink and float fractions were calculated by using elemental analysis and the mineral data on the starting oil shale. This approach was especially useful to rapidly material balance the minerals in the sink and float fractions from the many variable optimization runs required for the beneficiation reactions without having to obtain XRD patterns for every fraction. The combination of elemental analysis2 for wt 5% of Si, Al, Fe, Ca, Mg, Na, K, pyritic S, (1) Siskin, M.; Brons, G.; Payack, J. F., Jr. Energy Fuels 1987,1,248. (2) ASTM Procedures D 3682-78 (standardtest method for major and minor elements in coal and coke ash by atomic adsorption)used for ash mineral analysis, D 1374 for wt % ash, and D 2492 for sulfur forms. A Galbraith Laboratoriea in-house technique involving the evolution of COP and titration was used for wt % C032-.
0887-0624/89/2503-0085$01.50/0
Table I. Ash Mineral Analysis for Green River Oil Shale wt % of oxide wt % of oxide wt % of metal on ash on whole shale on whole shale 45.31 (SO2) 28.00 (SO2) 13.09 (Si) 4.35 (Fe203) 2.69 (Fe20,) 1.88 (Fe) 9.49 (A1203) 5.86 (A1203) 3.10 (Al) 24.03 (CaO) 14.85 (CaO) 10.61 (Ca) 8.12 (MgO) 5.02 (MgO) 3.01 (Mg) 2.08 (K2O) 1.29 (K2O) 1.07 (K) 3.01 (NazO) 1.86 (Na20) 1.38 (Na)
and C032-with XRD data from the starting shale for mineral analysis provided a simpler technique for mineral distribution determinations. The procedures for calculating quantitative mineral distributions are illustrated in the Experimental Section.
Experimental Section The oil shales were ground to pass 325 mesh (44 fim) and bulk loaded into standard X-ray cells made shallow by using a plastic spacer. The X-ray diffraction powder patterns were acquired by scanning from 2 to 70' (28). The XRD data were collected by using a Philips ADP 3600 diffractometer under standard conditions: Cu-Ka radiation, 40 kV, 40 mA. The carbonate minerah were then removed via acid washing, and a clay suspension and clay slides were prepared according to the procedure of Jackson? The identification of the mineral phases was verified, and semiquantitative mineral distributions in the samples were computed by using a Quant XRD program involving the normalization of peak areas. General Procedure for Calculating Quantitative Mineral Distributions. Illustrated f o r Green River Oil Shale. The ash mineral analysis obtained on a dry-weight basis (wt % oxide) is convered to a whole-shale basis and then to the weight percent of the elements present (Table I). Other analyses included the following: ash, 61.80 wt %; SO, on ash, 2.95 wt %; CO3&,24.80 w t %; pyritic S, 0.84 wt %. The next step involves converting the percentage of each element into percent minerals. The formulas and elemental compositions for the minerals identified by XRD in this sample of (3) Jackson, M. L. Soil Chemical Analysis-Advanced Course, 2nd ed.; published by the author: Madison, WI, 1979.
0 1989 American Chemical Society
Brons et al.
86 Energy & Fuels, Vol. 3, No. 1, 1989 Table 11. Formulas and Elemental Compositions of Minerals in Green River Oil Shale mineral formula elemental comDosition % Si, 46.75; % 0, 53.25 quartz SiOz albite NaAlSi30B % Na, 8.77; % Al, 10.29; % Si, 32.13; % 0, 48.81 calcite CaCOS % Ca, 40.05; % CO?-, 59.95; % c , 11.99 % Ca, 21.74; % Mg, 13.18; dolomite CaMg(C03)~ % CO?-, 65.08; % C, 13.02; % 0, 52.06 siderite FeCOS % Fe, 48.21; % CO?-, 51.79; % C, 10.36; % 0, 41.43 % Fe, 46.57; % S, 53.43 70 Na, 15.97; % Al, 18.74; % CO?-,41.68; % OH, 23.62; % C, 8.34; % 0, 55.37; % H, 1.39 illite (general) KA1z(Si3Al)Olo(OH)z% K, 9.82; % Al, 20.32; % Si, 21.16; % 0, 48.20; % OH, 8.54; % H, 0.50 analcime NaA1Si206.H20 % Na, 10.44; % Al, 12.26; % Si, 25.52; % HzO, 8.18; % 0, 50.87; % H,
pyrite dawsonite
FeSz NaAl(OH)zC03
0.91
Table IV. Mineral Composition of Raw Green River Oil Shale Obtained by Using XRD and Elemental Analysis (Organic Content by Difference) mineral compn, wt % mineral compn, wt % illite 10.9 pyrite 1.6 albite 13.7 quartz 13.2 dawsonite 0.6 dolomite 22.8 analcime 0.9 calcite 14.1 siderite 2.4 (organics 19.8)
amount of sodium present less the amounts of sodium as dawsonite and analcime. Illite, like most clay minerals, varies greatly in its composition. The general formula for illite in Green River formation oil shales is KAlz(Si3Al)Olo(OH)2.4XRD revealed that illite was the only mineral in the shale that contained potassium. The potassium concentration and the general formula for illite were used to calculate the concentration of illite. T o check the concentration of illite, the amount of silicon that exists in the illite can be determined separately. XRD provided a peak area ratio of quartz to illite of 21:17. This suggests that, for every gram of illite, there exists 1.24 g of quartz. From the ratio and the empirical formulas, with the associated silicon levels in illite and quartz, the amount of silicon that exists as quartz and as illite can be found.
Q = amount of quartz; Z = amount of illite; 1.241 = Q Table 111. Mineral Composition Calculations for Raw Green River Oil Shale pyrite: 0.84 g of S = 1.57 g of pyrite siderite: 1.88 g of K(tota1) - 0.73 g of Fe(pyrite) = 1.15 g of Fe = 2.39 g of siderite dolomite: 3.01 g of Mg(tota1) = 22.84 g of dolomite calcite: 10.61 g of Ca(tota1) - 4.96 g of Ca(do1omite) = 5.65 g of Ca = 4.11 g of calcite dawsonite: 24.80 g of CO$-(total) - 1.24 g of CO:-(siderite) 14.86 g of C032-(dolomite)- 8.46 g of C03"(calcite) = 0.24 g of COS2-= 0.58 g of dawsonite analcime: 0.58 g of dawsonite X 3/zn = 0.87 g of analcime albite: 1.38 g of Na(tota1) - 0.09 g of Na(dawsonite1 - 0.09 g of Na(ana1cime) = 1.20 g of Na = 13.68 g of albite illite (via K): 1.07 g of K(tota1) = 10.90 g of illite quartz: 6.15 g of Si = 13.15 g of quartz illite (via Si): 2.32 g of Si = 10.96 g of illite
XRD peak area ratio of ana1cime:dawsonite. Green River oil shale are given in Table 11. Trace minerals (e.g. potassium feldspar, ankerite) have been omitted. For simplicity, percentages will be discussed in terms of grams, assuming 100 g of the shale sample instead of 100%. Calculation values are given in Table 111. The only iron-bearing minerals found by XRD were pyrite and siderite. The amount of pyrite present can be determined by using the pyritic sulfur value. The total iron content less the amount of iron as pyrite yields the amount of iron that exists as siderite. Dolomite was the only magnesium-bearing mineral identified. Therefore, the total amount of magnesium was used to determine the dolomite concentration. Dolomite and calcite were the only calcium-bearing minerals identified. The total calcium content less that determined as dolomite yields the amount of calcium that exists as calcite. Dawsonite was determined by XRD to be the last of the four carbonate-containing minerals present in the sample. The total sodium content was not used to calculate for dawsonite because XRD revealed that analcime and albite, also sodium-bearing minerals, were present. The dawsonite concentration was determined by using the total CO2-content less the C032-in the siderite, dolomite, and calcite. XRD peak area ratios suggested that the ratio of analcime to dawsonite was 3:2. This ratio was used to determine the level of analcime. The reliance on XRD ratios of minerals is one major source of errors. Because the intensities of the bands were both small, using the ratio of dawsonite to analcime was preferable to using the ratio of dawsonite or analcime to albite (1:8) because the albite bands were much higher in intensity. Quantification by comparison of small and large peaks would yield ratios subject to larger errors. The concentration of albite is better determined by using the total
Q = x/0.4675 Z = y/0.2180
x = amount of Si as quartz y = amount of Si as illite
Subtracting the silicon levels in all of the above minerals (13.68 g of albite, 4.40 g of Si; 0.87 g of analcime, 0.22 g of Si) from the total silicon yields the amount of silicon that exists as both quartz and illite: 13.09 g of Si-4.62 g of Si(cum) = 8.47 g of Si, therefore, x + y = 8.47 g and 1.241 = ~10.4675. Solving for x and y gives 6.15 g and 2.32 g, respectively. The value for x as the amount of silicon that exists as quartz is used to calculate the quartz concentration. Using the y value to calculate for the amount of silicon that exists as illite serves as an internal check for the amount of illite calculated from the potassium value. These two values are identical (Table 111). To check the balance of the elements, the cumulative amount of aluminum found in the above calculated minerals was determined (3.84 wt %) and compared to that of the total aluminum (3.10 wt %) determined on the sampleaZThese values are in good agreement considering the propagation of errors that are encountered from a series of calculations such as these and from the use of the general clay formula for illite. As an alternative check on the calculations, the amount of organic matter in the sample can be used: 100 - % SO3 free ash - % C 0 2 = % organic matter
Applying this formula to the Green River oil shale sample yields 21.8 wt % organic matter (100- 60.0% S03-freeash - 18.2% Cod. The use of this formula neglects the losses of hydrates and/or hydroxyl groups associated with the minerals on ashing. T o correct the 21.8 wt % organic matter value, the amount of OH and/or adducted H20 in the illite, dawsonite and analcime (1.14 cumulative wt %) was subtracted to give a more accurate organic matter level of 20.7 wt % . Comparing this to the value determined from the mineral calculations (19.8 w t %) shows a difference of only 4%. The total mineral distribution determined for this sample of Green River oil shale is given in Table lV. The number of significant figures has been reduced because of the propagation of errors encountered when doing a series of calculations such as these involving elemental analysis. For the same reason, one might want to reduce the number of significant figures further. Illustrated for Rundle Ramsay Crossing Oil Shale. Calculating the wt % organic matter in Rundle oil shale is not as simple as the Green River oil shale (100 - % SO3-free ash (4) Smith, J. W. Geochemistry and Chemistry of Oil Shales; ACS Symposium Series 230; American Chemical Society: Washington, DC, 1983, p 225.
Mineral Distributions in Oil Shales Table V. Ash Mineral Analysis for Rundle Ramsay Crossing Oil Shale w t % of oxide w t % of oxide wt % of metal on ash on whole shale on whole shale 48.67 (SiOz) 22.75 (Si) 64.87 @ioz) 5.11 (FezO3) 3.57 (Fe) 6.81 (Fe203) 13.50 (A1203) 10.13 (A1203) 5.36 (Al) 5.02 (CaO) 3.76 (CaO) 2.69 (Ca) 2.60 (MgO) 1.57 (Mg) 3.47 (MgO) 1.12 (K) 1.80 (KZO) 1.35 (KZO) 1.03 (Na20) 0.76 (Na) 1.37 (NazO) % C02) because the clay content of the Rundle oil shale is much more complex. The clays in Rundle oil shale contain higher levels of hydrates and hydroxyl groups. In the case of Green River oil shale, it is not essential to account for the loss of water during ashing because illite, which contains relatively little water, is the only major clay mineral present. In the case of the Rundle oil shale, calculation of the wt % organic matter would yield a larger error unless the loas of hydrates and hydroxyl groups are accounted for. The ash oxide analyses (Table V) were first normalized to the 75.02 wt % ash determined on this sample. The weight percent oxides and weight percent elements on the whole shale were then calculated. Ten minerals were found by XRD in this sample of Rundle oil shale (Table VI). A Soxhlet extraction with water was carried out to determine the soluble salt content. Halite was the only soluble material extracted from the sample, and is included in Table VI. Other required analyses2 obtained on this sample include the following: pyritic S, 0.61 wt %; C1,0.24 wt %; CO:-, 5.30 wt %; SO3 on ash, 2.23 wt %. Calculation values are given in Table VII. The only iron-bearing minerals found by XRD were pyrite, siderite, and smectite. The amount of pyrite was determined by using the pyritic sulfur value. The distribution of the remaining iron as siderite and smectite (nontronite) cannot be determined a t this point and will be discussed later. The concentration of halite was determined by using the chloride level. This value corresponded to the weight loss of the sample during water extraction. XRD revealed that the sodium-bearing mineral plagioclase, which is a mixed calcium and sodium feldspar, also existed. XRD was not able to determine how much of the plagioclase existed as calcium or sodium feldspar. T o determine these levels, each feldspar was first calculated individually (Table VI). The difference in the total sodium concentration and the sodium that exists as the halite gives the level of sodium that exists as sodium feldspar (albite). The calcium-bearing minerals in this sample, as determined by XRD, were calcium feldspar, calcite, dolomite, and smectite. The distribution of these cannot be determined at this point and will be discussed later. XRD determined that three carbonate minerals existed in this sample: calcite, dolomite, and siderite. The total carbonate level was used to determine maximum levels, or upper limits, of each carbonate mineral, assuming that all of the carbonate existed as each mineral. The total carbonate mineral level is between 8.14
Energy &Fuels, Vol. 3, No. 1, 1989 87 and 10.23 g (Table VII). This range is narrowed when the iron content is examined. The previously determined pyrite content revealed that 3.04 g of iron exists as siderite and nontronite. Assuming that all of the iron exists as siderite only, the upper limit of the siderite can be determined (6.31 9). Therefore, the amount of siderite cannot exceed 6.31 g, which shows that the 10.23 g of siderite possibility is incorrect. This reduces the range of total carbonate minerals present (8.14-8.84 g). Therefore, the total carbonate mineral content is 8.49 f 0.35 g. The distribution of carbonate minerals was determined by using the peak ratios found by XRD (ca1cite:dolomite:siderlite = 5:2:3) and the total mineral content (8.49 g). This Rundle shale sample, unlike the Green River sample, contains more than one clay mineral. The general formulas for the clays were used in determining concentration levels with the awareness that this will lead to increased error. XRD revealed that the only mineral containing potassium was illite. From the general formula for illite, its concentration was determined. The smectites in this sample were determined to be rich in magnesium, calcium, and iron. For simplicity, the general formulas for nontronite and montmorillonite were used. The level of iron that exists as nontronite was determined by subtracting the iron that existed in the pyrite and siderite from the total iron determined in the sample. the level of magnesium as montmorillonite was determined by subtracting the magnesium in dolomite from the total magnesium. The values for nontronite and montmorillonite were added to yield the total concentration of smectites: 21.73 g. The remaining minerals to be quantified are quartz, kaolinite, and calcium feldspar (as plagioclase). Subtracting the calcium found in the calcite, dolomite, and smectite from the total calcium concentration yields the amount of calcium that exists as calcium feldspar. Combining the levels of sodium and calcium feldspar yields the level of plagioclase: 10.72 g. The total aluminum content less the amounts of aluminum determined in the illite, smectite, and plagioclase yields the amount of aluminum that exists as kaolinite. Quartz was calculated from the balance of silicon determined by subtracting the silicon present in the above minerals from the total silicon. The distribution of minerals in this Rundle Ramsay Crossing oil shale is summarized in Table VIII. As with the Green River results, the unwarranted number of significant figures has been reduced. The total mineral levels (79.5 wt % ) subtracted from 100 yields the organic matter content of the shale: 20.5 wt %. As stated earlier, the alternative formula used for calculating the weight percent of organic matter in resource materials neglects losses of hydrates and hydroxyl groups from the clays on ashing. Using the formula on the Rundle sample (100 - 73.35% SOs-free ash - 3.89% COz) yields 22.76% organic matter/hydrates/ hydroxyls. Calculating the amounts of hydrates and hydroxyls in the clay minerals determined above (3.64%) and subtracting from the 22.76% value yields 19.12 wt % organic matter. This is within 7% of the weight percent of organic matter determined above. This range of 19.1-20.5 wt % organic matter is in good agreement with values determined by others for Rundle oil shales from the Lower Ramsay Crossing seam.6
Table VI. Formulas and Elemental Compositions of Minerals in Rundle Ramsay Crossing Oil Shale mineral formula elemental comDosition SiOz % Si, 46.75; % 0, 53.25 quartz Cd1&~016/Nd1Si& % Ca, 5.13; % Na, 2.94; % Al, 10.37; % Si, 32.38; % 0, 49.18 plagioclase NaA1Si308 % Na, 8.77; % Al, 10.29; % Si, 32.13; % 0, 48.81 sodium feldspar cd1zsi6016 % Ca, 7.73; % Al, 10.41; % Si, 32.50; % 0, 49.37 calcium feldspar calcite % Ca, 40.05; % CO?-, 59.95; % C, 11.95; % 0, 48.00 CaCO, % Ca, 21.74; % Mg, 13.18; % C032-, 65.08; % C, 13.02; % 0, 52.06 dolomite CaMg(C03)z % Fe. 48.21: % CO?. 51.79: % C. 10.36: % 0. 41.43 siderite FeC09 pyrite FeSz 5% Fe; 46.571 % S, g3.43 illite (general) % K, 9.82; % Al, 20.32; % Si, 21.16; % 0, 48.20; % H, 0.50; KAl2(Si3Al)Olo(OH)z or % HzO, 5.00 montmorillonite % Mg, 9.40; % Al, 6.96; % Si, 28.97; % 0, 41.26; % OH, 8.77; Mgo,6A1MgSi1010(OH)2.Hz0 % HzO, 4.64 (general) % Ca, 4.40; % Fe(II), 24.55; % Al, 5.93; % Si, 18.52; % 0, 45.72; C~,6Fe(II)zSi3A1010(OH)z~Hz0 nontronite % OH, 7.47; % H,O, 3.96 (general) % Al, 20.90; % Si, 21.76; % 0, 55.78; Yo H, 0.02, % HzO, 12.63 kaolinite (general) A1203.2Si02.2Hz0 % Na, 39.34; % C1, 60.66 halite NaCl '
88 Energy & Fuels, Vol. 3, No. 1, 1989 Table VII. Mineral Composition Calculations for Rundle Ramsay Crossing Oil Shale pyrite: 0.61 g of ,S = 1.14 g of pyrite iron balance: 3.57 g of Fe(tota1) - 0.53 g of Fe(pyrite) = 3.04 g of Fe halite: 0.24 g of C1 = 0.40g of halite sodium feldspar: 0.76 g of Na(total) - 0.16 g of Na(ha1ite) = 0.60 g of Na = 6.84 g of sodium feldspar co2- minerals: upper limits, 5.30g of co32-=/0.5995= 8.84 g of calcite, 5.30 g of C032-/0.6508= 8.14 g of dolomite, or 5.30 g of C02-/0.5179= 10.23 g of siderite; actual, 0.5 X 8.49 = 4.25 g of calcite, 0.2 X 8.49 = 1.70 g of dolomite, and 0.3 X 8.49 = 2.55 g of siderite illite: 1.12 g of K = 11.41 g of illite nontronite: 3.57 g of Fe(tota1) - 0.53 g of Fe(pyrite) - 1.23 g of Fe(siderite) = 1.81 g of Fe = 7.37 g of nontronite montmorillonite: 1.57 g of Mg(tota1) - 0.22 g of Mg(do1omite) = 1.35 g of Mg = 14.36 g of montmorillonite calcium feldspar: 2.69 g of Ca(tota1) - 0.32g of Ca(nontronite) 0.37g of Ca(do1omite) - 1.70 g of Ca(calcite) = 0.32g of Ca = 3.88 g of calcium feldspar kaolinite: 5.36 g of Al(tota1) - 0.70 g of Al(sodium feldspar) 2.32 g of Al(i1lite) - 1.00 g of Al(montmoril1onite)- 0.44 g of Al(nontronite) - 0.40 g of Al(ca1cium feldspar) = 0.50 g of A1 = 2.39 g of kaolinite quartz: 22.75 g of &(total) - 2.20 g of Si(sodium feldspar) - 2.41 g of Si(illite) - 4.16 g of Si(montmoril1onite) - 1.36 g of Si(nontronite1 1.26 g of %(calcium feldspar) - 0.52 g of Si(kao1inite) = 10.84 g of Si = 23.19 g of quartz
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Table VIII. Mineral Composition of Rundle Ramsay Crossing Oil Shale Obtained by Using XRD and Elemental Analysis (Organic Content by Difference) mineral compn, w t % mineral compn, w t % quartz 23.2 dolomite 1.7 plagioclase 10.7 calcite 4.3 illite 11.4 siderite 2.6 smectite 21.7 pyrite 1.1 kaolinite 2.4 halite 0.4 (organics 20.5)
Results and Discussion The mineral distributions in raw Green River and Rundle Ramsay Crossing oil shales were determined by using a combination of X-ray diffraction (XRD) and elemental analysis as described in the Experimental Section and are given in Tables IV and VIII, respectively. Previous work' describing a beneficiation procedure for the separation of minerals from Green River oil shale provided product samples that varied greatly in mineral composition. To monitor the changes, a normative calculation approach using chemical data was developed that eliminated the need for XRD analysis of every fraction from every treatment. Quantification of the mineral composition in the raw Green River oil shale provided the necessary base from which distributions could be monitored. The product fractions from each treatment could then be analyzed with much less effort. The distribution of illite, for example, during fractionation treatments could be monitored via potassium analysis only. To illustrate how the method is used, a sample of Green River oil shale after being subjected to the aqueous ammonium sulfate beneficiation treatment' was examined. The treatment produced a kerogen-enriched float fraction (53.1 w t % organic matter) and a mineral-enriched sink fraction (4.8 wt % organic matter). From elemental analyses2 (Table IX) and mineral data on the raw shale, the mineral concentrations in each fraction and recoveries (5)Parks, T.;Lynch, L. J.; Webster, D. S. Prepr. Pap.-Am. Chem.
soc., Diu. Fuel Chem. 1986, 30, 247-255.
Brons et al. Table IX. Elemental Analysis from Ammonium Sulfate Enrichment of Green River Oil Shale with Toluene at 85 "C for 72 h anal.. wt % untreated float sink Si 13.09 7.04 31.29 Fe 1.88 3.28 2.14 A1 3.10 1.71 7.13 Ca 10.61 5.28 0.18 1.45 0.07 Mg 3.01 K 1.07 0.91 2.54 Na 1.38 0.42 2.46 C as C0324.96 2.28
